In an analysis using a liquid chromatograph, an autosampler is used to automatically introduce a plurality of samples into analytical columns in a predetermined order. As an autosampler, an autosampler adopting a so-called total-volume injection method is widely used in which a predetermined amount of sample is collected from a sample container and the total volume thereof is injected into an analysis flow path through which a mobile phase flows.
In injecting a sample by a total-volume injection method, initially, a predetermined amount of sample is sucked from a sample container with a needle and is retained in a sample loop connected to a base end portion of the needle. Thereafter, the needle is inserted into a sample injection port and a flow path switching operation by a flow path switching valve is performed to thereby interpose the sample loop between a liquid feeding device that feeds a mobile phase and an analytical column. With this, the entire sample retained in the sample loop is transferred to and introduced into the analytical column by the mobile phase from the sample container (see Patent Document 1).
As other injection methods, there are some injection methods adopting a fixed loop injection method. In the method, a predetermined amount of sample is sucked from a sample container through a needle and retained in a sample loop for sucking a sample connected to a base end portion of the needle. After that, the needle is inserted into a sample injection port to retain a necessary amount of sample in the sample loop for a sample injection connected via a flow path switching valve. Thereafter, by performing a switching flow path operation by the flow path switching valve, the sample loop for a sample injection is interposed between a liquid feeding device for feeding a mobile phase and an analytical column. As a result, the sample retained in the sample loop for a sample injection is transferred to and introduced into the analytical column by the mobile phase from the sample container.
The above-described two injection methods have the following advantages and disadvantages. In the total-volume injection method, since the entire amount of sample retained in the sample loop is injected into the analysis flow path, there is a merit that there is no sample loss. On the other hand, in the fixed loop injection method, since a part of the sample retained in the sample loop for a sample injection is discarded, it is particularly disadvantageous in the case of a valuable sample.
Further, in the total-volume injection method, the flow path connected to the base end portion of the needle is formed long to ensure the mobility of the needle, resulting in a large dead volume, which in turn causes disadvantages that a sample diffusion and a gradient delay are likely to occur. On the other hand, in the fixed loop injection method, the sample loop for a sample injection is formed independent of the needle. Therefore, there are merits that a dead volume is smaller than that in the total-volume injection method, the peak of the chromatogram becomes shaper than that of the total-volume injection method, and the analysis speed is high.